Image sensor and manufacturing method therefore

ABSTRACT

An image sensor including a substrate, a light sensing device, a storage node, a buried gate structure, and a first light shielding layer is provided. The light sensing device is disposed in the substrate. The storage node is disposed in the substrate. The storage node and the light sensing device are separated from each other. The buried gate structure includes a buried gate and a first dielectric layer. The buried gate is disposed in the substrate and covers at least a portion of the storage node. The first dielectric layer is disposed between the buried gate and the substrate. The first light shielding layer is disposed on the buried gate and is located above the storage node. The first light shielding layer is electrically connected to the buried gate.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Taiwan applicationserial no. 107130190, filed on Aug. 29, 2018. The entirety of theabove-mentioned patent application is hereby incorporated by referenceherein and made a part of this specification.

BACKGROUND OF THE INVENTION Field of the Invention

The invention relates to a semiconductor device and a manufacturingmethod therefore, and particularly relates to an image sensor and amanufacturing method therefore.

Description of Related Art

Currently, there are some types of image sensors (e.g., the globalshutter image sensor) having a storage node for storing signals.However, stray light interferes with the signals stored in the storagenode. Therefore, how to effectively prevent stray light interference isthe goal of ongoing research and development.

SUMMARY OF THE INVENTION

The invention provides an image sensor and a manufacturing methodtherefore, which effectively prevents stray light interference.

The invention provides an image sensor including a substrate, a lightsensing device, a storage node, a buried gate structure, and a firstlight shielding layer. The light sensing device is disposed in thesubstrate. The storage node is disposed in the substrate. The storagenode and the light sensing device are separated from each other. Theburied gate structure includes a buried gate and a first dielectriclayer. The buried gate is disposed in the substrate and covers at leasta portion of the storage node. The first dielectric layer is disposedbetween the buried gate and the substrate. The first light shieldinglayer is disposed on the buried gate and located above the storage node.The first light shielding layer is electrically connected to the buriedgate.

According to an embodiment of the invention, in the aforementioned imagesensor, a portion of the buried gate may be located in the substratebetween the light sensing device and the storage node.

According to an embodiment of the invention, in the aforementioned imagesensor, a material of the first light shielding layer is, for example, ametal or a metal compound.

According to an embodiment of the invention, the aforementioned imagesensor may further include a second light shielding layer. The secondlight shielding layer is disposed on the first light shielding layer.

According to an embodiment of the invention, in the aforementioned imagesensor, the first light shielding layer may have an extending portion.The extending portion extends into the buried gate.

According to an embodiment of the invention, in the aforementioned imagesensor, the extending portion may be extended to the first dielectriclayer.

According to an embodiment of the invention, in the aforementioned imagesensor, the extending portion may be located between the light sensingdevice and the storage node.

According to an embodiment of the invention, the aforementioned imagesensor may further include a third light shielding layer. The thirdlight shielding layer is disposed between the first light shieldinglayer and the buried gate.

According to an embodiment of the invention, the aforementioned imagesensor may further include a second dielectric layer. The seconddielectric layer is disposed between the first light shielding layer andthe buried gate. The extending portion passes through the seconddielectric layer and extends into the buried gate.

According to an embodiment of the invention, the aforementioned imagesensor may further include a pinning layer. The pinning layer isdisposed in the substrate and located between the light sensing deviceand a surface of the substrate.

According to an embodiment of the invention, the aforementioned imagesensor may further include a gate structure and a floating diffusionregion. The gate structure includes a gate and a third dielectric layer.The gate is disposed on the substrate and located at one side of theburied gate away from the light sensing device. The gate and the buriedgate are separated from each other. The third dielectric layer isdisposed between the gate and the substrate. The floating diffusionregion is disposed in the substrate and located at one side of the gatestructure away from the buried gate structure.

According to an embodiment of the invention, the aforementioned imagesensor may further include a color filter layer and a microlens. Thecolor filter layer is disposed above the light sensing device. Themicrolens is disposed on the color filter layer.

The invention provides an image sensor manufacturing method includingthe following steps. A substrate is provided. A light sensing device isformed in the substrate. A storage node is formed in the substrate. Thestorage node and the light sensing device are separated from each other.A buried gate structure is formed in the substrate. The buried gatestructure includes a buried gate and a first dielectric layer. Theburied gate is disposed in the substrate and covers at least a portionof the storage node. The first dielectric layer is disposed between theburied gate and the substrate. A first light shielding layer is formedon the buried gate. The first light shielding layer is located above thestorage node, and electrically connected to the buried gate.

According to an embodiment of the invention, the manufacturing method ofthe aforementioned image sensor may further include forming a secondlight shielding layer on the first light shielding layer.

According to an embodiment of the invention, in the manufacturing methodof the aforementioned image sensor, the first light shielding layer mayhave an extending portion. The extending portion extends into the buriedgate.

According to an embodiment of the invention, the manufacturing method ofthe aforementioned image sensor may further include forming a thirdlight shielding layer between the first light shielding layer and theburied gate.

According to an embodiment of the invention, in the manufacturing methodof the aforementioned image sensor may further include forming a seconddielectric layer between the first light shielding layer and the buriedgate. The extending portion passes through the second dielectric layerand extends into the buried gate.

According to an embodiment of the invention, the manufacturing method ofthe aforementioned image sensor may further include forming a pinninglayer in the substrate. The pinning layer is located between the lightsensing device and a surface of the substrate.

According to an embodiment of the invention, the manufacturing method ofthe aforementioned image sensor may further include the following steps.The gate structure is formed on the substrate. The gate structureincludes a gate and a third dielectric layer. The gate is disposed onthe substrate and located at one side of the buried gate away from thelight sensing device. The gate and the buried gate are separated fromeach other. The third dielectric layer is disposed between the gate andthe substrate. The floating diffusion region is formed in the substrate.The floating diffusion region is located at one side of the gatestructure away from the buried gate structure.

According to an embodiment of the invention, the manufacturing method ofthe aforementioned image sensor may further include the following steps.The color filter layer is formed above the light sensing device. Themicrolens is formed on the color filter layer.

Based on the above, in the aforementioned image sensor and themanufacturing method therefore, the buried gate is disposed in thesubstrate and covers at least a portion of the storage node. The firstlight shielding layer is disposed on the buried gate and located abovethe storage node. Therefore, the first light shielding layer may blockstray light from illuminating the storage node to effectively preventstray light interference.

To make the above features and advantages of the disclosure morecomprehensible, embodiments accompanied with drawings are described indetail as follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A to FIG. 1F are cross-sectional views of a manufacturing processof an image sensor according to an embodiment of the invention.

FIG. 2 is a cross-sectional view of an image sensor according to anotherembodiment of the invention.

FIG. 3A to FIG. 3C are cross-sectional views of a manufacturing processof an image sensor according to an embodiment of the invention.

FIG. 4 is a cross-sectional view of an image sensor according to anotherembodiment of the invention.

FIG. 5A to FIG. 5C are cross-sectional views of a manufacturing processof an image sensor according to another embodiment of the invention.

DESCRIPTION OF THE EMBODIMENTS

FIG. 1A to FIG. 1F are cross-sectional views of a manufacturing processof an image sensor according to an embodiment of the invention.

Please refer to FIG. 1A, a substrate 100 is provided. The substrate 100is, for example, a silicon substrate. The substrate 100 may have anisolation structure 102. The isolation structure 102 is, for example, ashallow trench isolation (STI) structure. A material of the isolationstructure 102 is, for example, silicon oxide. A mask structure 104 maybe formed on the substrate 100. The mask structure 104 may be a singlelayer structure or a multilayer structure. In the present embodiment,the mask structure 104 is exemplified by the multilayer structure, butthe invention is not limited thereto. For instance, the mask structure104 includes a mask layer 104 a and a mask layer 104 b. The mask layer104 a is disposed on the substrate 100. A material of the mask layer 104a is, for example, silicon oxide. The mask layer 104 b is disposed onthe mask layer 104 a. A material of the mask layer 104 b is, forexample, silicon nitride.

Besides, the substrate 100 may have a first conductive type.Hereinafter, the first conductive type and the second conductive typemay be one and the other of the P-type conductive type and the N-typeconductive type, respectively. In the present embodiment, the firstconductive type is exemplified by the P-type conductive type, and thesecond conductive type is exemplified by the N-type conductive type, butthe invention is not limited thereto.

A light sensing device 106 is formed in the substrate 100. The lightsensing device 106 may be a photodiode. In the present embodiment, thelight sensing device 106 is, for example, a doped region of the secondconductive type (e.g., N-type), such as a well region of the secondconductive type. A forming method of the light sensing device 106 is,for example, ion implantation.

A storage node 108 is formed in the substrate 100. The storage node 108and the light sensing device 106 are separated from each other. Thestorage node 108 is, for example, a doped region of the secondconductive type (e.g., N-type), such as the well region of secondconductive type. A forming method of the storage node 108 is, forexample, ion implantation.

A pinning layer 110 may be formed in the substrate 100. The pinninglayer 110 is located between the light sensing device 106 and a surfaceof the substrate 100. The pinning layer 110 may be used to reduce darkcurrent. The pinning layer 110 is, for example, a heavily doped regionof the first conductive type (e.g., P-type). A forming method of thepinning layer 110 is, for example, ion implantation.

In addition, people skilled in the art may determine the forming orderof the light sensing device 106, the storage node 108, and the pinninglayer 110 according to process requirements.

A patterned photoresist layer 112 may be formed on the mask layer 104. Amaterial of the patterned photoresist layer 112 is, for example, apositive photoresist material or a negative photoresist material. Aforming method of the patterned photoresist layer 112 is, for example, alithography process.

A recess 114 may be formed in the substrate 100. The recess 114 mayexpose the storage node 108. A forming method of the recess 114 is, forexample, removing a portion of the mask layer 104 and a portion of thesubstrate 100 by using the patterned photoresist layer 112 as a mask.The removing method of a portion of the mask layer 104 and a portion ofthe substrate 100 is, for example, a dry etching method or a wet etchingmethod.

Please refer to FIG. 1B, the patterned photoresist layer 112 is removed.The removing method of the patterned photoresist layer 112 is, forexample, a dry stripping method or a wet stripping method.

A dielectric layer 116 may be formed on a surface of the recess 114. Amaterial of the dielectric layer 116 is, for example, silicon oxide,silicon nitride or a combination thereof. A forming method of thedielectric layer 116 is, for example, thermal oxidation, nitridation, orchemical vapor deposition.

A conductive layer 118 filling up the recess 114 may be formed. Amaterial of the conductive layer 118 is, for example, doped polysilicon,but the invention is not limited thereto. A forming method of theconductive layer 118 is, for example, chemical vapor deposition. Theconductive layer 118 may have the first conductive type or the secondconductive type. In the present embodiment, the conductive layer 118 isexemplified by having the second conductive type (e.g., N-type).

Please refer to FIG. 1C, the conductive layer 118 outside the recess 114may be removed to form a buried gate 118 a in the substrate 100. Theremoving method of the conductive layer 118 outside the recess 114 isthat, for example, the mask layer 104 is used as a stop layer, and achemical mechanical polishing process is performed on the conductivelayer 118.

Thereby, a buried gate structure 120 may be formed in the substrate 100.The buried gate structure 120 includes the buried gate 118 a and thedielectric layer 116. The buried gate 118 a is disposed in the substrate100 and covers at least a portion of the storage node 108. A portion ofthe storage node 108 may be located in the substrate 100 at one side ofthe buried gate 118 a away from the light sensing device 106 and may beextended to the surface of the substrate 100. The dielectric layer 116is disposed between the buried gate 118 a and the substrate 100. In thepresent embodiment, although the buried gate structure 120 is formed bythe aforementioned methods, the invention is not limited thereto.

Please refer to FIG. 1D, the mask layer 104 may be removed. The removingmethod of the mask layer 104 is, for example, the wet etching method. Anetchant used in the wet etching method is, for example, phosphoric acidor hydrofluoric acid. People skilled in the art may choose a suitableetchant according to the material of the mask layer 104.

A gate structure 122 may be formed on the substrate 100. The gatestructure 122 includes a gate 124 and a dielectric layer 126. The gatestructure 122 may further include a spacer 128. The gate 124 is disposedon the substrate 100 and located at one side of the buried gate 118 aaway from the light sensing device 106. The gate 124 and the buried gate118 a are separated from each other. The dielectric layer 126 isdisposed between the gate 124 and the substrate 100. The spacer 128 isdisposed on a sidewall of the gate 124. A forming method of the gatestructure 122 may be carried out by a method known to people skilled inthe art and are not further illustrated here.

A floating diffusion region 130 may be formed in the substrate 100. Thefloating diffusion region 130 is located at one side of the gatestructure 122 away from the buried gate structure 120. The floatingdiffusion region 130 may have the second conductive type (e.g., N-type).A forming method of the floating diffusion region 130 is, for example,ion implantation.

Please refer to FIG. 1E, a light shielding layer 132 is formed on theburied gate 118 a. The light shielding layer 132 is located above thestorage node 108 and electrically connected to the buried gate 118 a. Amaterial of the light shielding layer 132 is, for example, a metal or ametal compound (e.g., a metal silicide). In the present embodiment, thematerial of the light shielding layer 132 is exemplified by the metalsilicide. The metal silicide is, for example, cobalt silicide or nickelsilicide. A forming method of the light shielding layer 132 is, forexample, performing a salicidation process. In another embodiment, theforming method of the light shielding layer 132 may also be chemicalvapor deposition or physical vapor deposition.

Additionally, a metal silicide layer 134 may be formed on the gate 124.The gate structure 122 may further include the metal silicide layer 134.A material of the metal silicide layer 134 is, for example, a metalsilicide such as cobalt silicide or nickel silicide. A forming method ofthe metal silicide layer 134 is, for example, performing thesalicidation process. The metal silicide layer 134 and the lightshielding layer 132 may be formed by the same or different process.Under the condition that the material of the light shielding layer 132is the metal silicide, the metal silicide layer 134 and the lightshielding layer 132 may be formed by the same process. For example, asalicide block layer SAB exposing the buried gate 118 a and the gate 124may be formed on the substrate 100, and then the light shielding layer132 and the metal silicide layer 134 may be respectively formed on theburied gate 118 a and the gate 124 by the salicidation process. Inanother embodiment, in the step of forming the salicide block layer SAB,the salicide block layer SAB may extend on a portion of the buried gate118 a to cover a portion of the buried gate 118 a, thereby helping toprevent the subsequently formed light shielding layer 132 from bridgingwith the substrate 100.

Please refer to FIG. 1F, a dielectric layer 136 covering the buried gatestructure 120 and the gate structure 122 may be formed. The dielectriclayer 136 may be a single layer structure or a multilayer structure. Amaterial of the dielectric layer 136 is, for example, silicon oxide,silicon nitride or a combination thereof. A forming method of thedielectric layer 136 is, for example, chemical vapor deposition.

An interconnect structure 138 and an interconnect structure 140 may beformed in the dielectric layer 136. The interconnect structure 138 maybe electrically connected to the buried gate 118 a via the lightshielding layer 132. The interconnect structure 140 may be electricallyconnected to the gate 128 via the metal silicide layer 134. Theinterconnect structure 138 and the interconnect structure 140 mayrespectively include a contact, a conductive line, or a combinationthereof. A material of the interconnect structure 140 is, for example,copper, aluminum, or tungsten. A method of forming the interconnectstructure 140 is, for example, the damascene process or a combination ofthe deposition process, the lithography process, and the etchingprocess. In addition, the number of layers of the interconnect structure138 and the number of layers of the interconnect structure 140 may beadjusted according to product requirements and may not be limited to thenumber of layers shown in the drawings.

A color filter layer 142 may be formed above the light sensing device106. In the present embodiment, the color filter layer 142 may be formedon the dielectric layer 136. The color filter layer 142 is, for example,a red filter layer, a green filter layer, or a blue filter layer. Amaterial of the color filter layer 142 is, for example, a photoresistmaterial, and a forming method of the color filter layer 142 may beperformed by spin coating, alignment, exposure, development, etc., whichare well known to people skilled in the art and are not furtherillustrated herein.

A microlens 144 may be formed on the color filter layer 142. A materialof the microlens 144 is, for example, a photoresist material. A formingmethod of the microlens 144 is, for example, spin-coating a microlensmaterial layer (not shown) first, performing the lithography process onthe microlens material layer by using a mask and applying hightemperature to heat baking the microlens material layer into a circulararc lens shape, or the other forming method, such as spin coating,alignment, exposure, development, etching, etc., which are well known topeople skilled in the art and are not further illustrated herein.

Hereinafter, an image sensor 146 of the present embodiment isillustrated by FIG. 1F. Moreover, although the forming method of theimage sensor 146 is illustrated as an example of the aforementionedmethod, the invention is not limited thereto.

Please refer to FIG. 1F, the image sensor 146 includes the substrate100, the light sensing device 106, the storage node 108, the buried gatestructure 120, and the light shielding layer 132. The image sensor 146may be a global shutter image sensor, but the invention is not limitedthereto. The light sensing device 106 is disposed in the substrate 100.The storage node 108 is disposed in the substrate 100. The storage node108 and the light sensing device 106 are separated from each other. Aportion of the storage node 108 may be located in the substrate 100 atone side of the buried gate 118 a away from the light sensing device 106and may extend to the surface of the substrate 100. The buried gatestructure 120 includes the buried gate 118 a and the dielectric layer116. The buried gate 118 a is disposed in the substrate 100 and coversat least a portion of the storage node 108. A portion of the buried gate118 a may be located in the substrate 100 between the light sensingdevice 106 and the storage node 108. The dielectric layer 116 isdisposed between the buried gate 118 a and the substrate 100. The lightshielding layer 132 is disposed on the buried gate 118 a and locatedabove the storage node 108. The light shielding layer 132 iselectrically connected to the buried gate 118 a.

The image sensor 146 may further include at least one of the pinninglayer 110, the gate structure 122, the floating diffusion region 130,the dielectric layer 136, the interconnect structure 138, theinterconnect structure 140, the color filter layer 142, and themicrolens 144. The pinning layer 110 is disposed in the substrate 100and located between the light sensing device 106 and the surface of thesubstrate 100. The gate structure 122 includes the gate 124 and thedielectric layer 126. The gate 124 is disposed on the substrate 100 andlocated at one side of the buried gate 118 a away from the light sensingdevice 106. The gate 124 and the buried gate 118 a are separated fromeach other. The dielectric layer 126 is disposed between the gate 124and the substrate 100. The floating diffusion region 130 is disposed inthe substrate 100 and located at one side of the gate structure 122 awayfrom the buried gate structure 120. The dielectric layer 136 covers theburied gate structure 120 and the gate structure 122. The interconnectstructure 138 and the interconnect structure 140 are located in thedielectric layer 136 and electrically connected to the buried gate 118 aand the gate 124, respectively. The color filter layer 142 is disposedabove the light sensing device 106. In the present embodiment, the colorfilter layer 142 may be disposed on the dielectric layer 136. Themicrolens 144 is disposed on the color filter layer 142.

In addition, the material, the arrangement, the conductive type, theforming method, and the effect of each component in the image sensor 146have been illustrated in detail in the aforementioned embodiments, andthe illustrations are not repeated here.

Based on the aforementioned embodiment, in the image sensor 146 and themanufacturing method thereof, the buried gate 118 a is disposed in thesubstrate 100 and covers at least a portion of the storage node 108. Thelight shielding layer 132 is disposed on the buried gate 118 a andlocated above the storage node 108. Therefore, the light shielding layer132 blocks the stray light from illuminating the storage node 108 toeffectively prevent stray light interference.

FIG. 2 is a cross-sectional view of an image sensor according to anotherembodiment of the invention.

The differences between the manufacturing method of an image sensor 200of FIG. 2 and the manufacturing method of the image sensor 146 of FIG.1F are as below. Please refer to FIG. 2, after the step of FIG. 1E isperformed, a light shielding layer 202 may be formed on the lightshielding layer 132. A material of the light shielding layer 202 is, forexample, a metal or a metal compound such as titanium (Ti), titaniumnitride (TiN), tantalum (Ta), tantalum nitride (TaN), tungsten (W) oraluminum (Al). A forming method of the light shielding layer 202 is, forexample, a combination of the deposition process, the lithographyprocess, and the etching process. In addition, a method of subsequentlycompleting the image sensor 200 may be referred to the illustrations ofFIG. 1F, and the illustrations thereof are not repeated here.

Please refer to FIG. 1F and FIG. 2, compared to the image sensor 146,the image sensor 200 may further include the light shielding layer 202.The light shielding layer 202 is disposed on the light shielding layer132. The interconnect structure 138 may be electrically connected to theburied gate 118 a via the light shielding layer 132 and the lightshielding layer 202. In addition, the arrangements, the materials, theforming methods, and the effects of other components in the image sensor200 have been illustrated in detail in the aforementioned embodiments,and the illustrations thereof are not repeated here.

Based on the aforementioned embodiment, since the image sensor 200further has the light shielding layer 202 apart from having the lightshielding layer 132, the stray light may be more effectively blockedfrom illuminating the storage node 108 to further prevent stray lightinterference.

FIG. 3A to FIG. 3C are cross-sectional views of a manufacturing processof an image sensor according to an embodiment of the invention. FIG. 3Ato FIG. 3C are cross-sectional views of the manufacturing processsubsequent to the step of FIG. 1E.

Please refer to FIG. 3A, after the steps of FIG. 1E are performed, anopening 300 may be formed in the light shielding layer 132 and theburied gate 118 a. The opening 300 may expose buried gate 118 a. Aforming method of the opening 300 is, for example, removing a portion ofthe light shielding layer 132 and a portion of the buried gate 118 a bythe lithography process and the etching process.

Please refer to FIG. 3B, a light shielding layer 302 filling in theopening 300 may be formed on the light shielding layer 132. As such, thelight shielding layer 302 may be formed on the buried gate 118 a. Thelight shielding layer 302 is located above the storage node 108 andelectrically connected to the buried gate 118 a. The light shieldinglayer 302 may have an extending portion 302 a. The extending portion 302a extends into the buried gate 118 a. The extending portion 302 a may belocated between the light sensing device 106 and the storage node 108. Aforming method of the light shielding layer 302 is, for example, acombination of the deposition process, the lithography process, and theetching process. The material of the light shielding layer 302 is, forexample, a metal or metal compound such as Ti, TiN, Ta, TaN, W or Al.

In the present embodiment, although the light shielding layer 302 isillustrated as an example of filling up the opening 300, the inventionis not limited thereto. In another embodiment, under the condition thatthe thickness of the light shielding layer 302 is thinner, the lightshielding layer 302 may not fill up the opening 300.

Please refer to FIG. 3C, the dielectric layer 136, the interconnectstructure 138, the interconnect structure 140, the color filter layer142, and the microlens 144 may be formed on the substrate 100. Themanufacturing methods of the dielectric layer 136, the interconnectstructure 138, the interconnect structure 140, the color filter layer142 and the microlens 144 in an image sensor 304 of FIG. 3B may bereferred to the illustrations of FIG. 1F, and the illustrations thereofare not repeated here.

Further, in the aforementioned manufacturing method of the image sensor304, although the light shielding layer 132 may be formed between thelight shielding layer 302 and the buried gate 118 a, the invention isnot limited thereto. In another embodiment, the light shielding layer132 may not be formed in the manufacturing method of the image sensor304.

Hereinafter, the image sensor 304 of the present embodiment isillustrated with reference to FIG. 3C. Further, although a formingmethod of the image sensor 304 is illustrated as an example of theaforementioned method, the invention is not limited thereto.

Please refer to FIG. 3C. The image sensor 304 includes a light shieldinglayer 302 and may further optionally include the light shielding layer132. The light shielding layer 302 is disposed on the buried gate 118 aand located above the storage node 108. The light shielding layer 302 iselectrically connected to the buried gate 118 a. The light shieldinglayer 302 has the extending portion 302 a. The extending portion 302 aextends into the buried gate 118 a. The extending portion 302 a may belocated between the light sensing device 106 and the storage node 108.The light shielding layer 132 is disposed between the light shieldinglayer 302 and the buried gate 118 a. In addition, the materials, thearrangements, the conductive types, the forming methods, and the effectsof other components of the image sensor 304 in FIG. 3C have beenillustrated in detail in the aforementioned embodiments, and theillustrations are not repeated here.

Based on the aforementioned embodiment, in the image sensor 304 and themanufacturing method thereof, the light shielding layer 302 may have theextending portion 302 a. In this way, in addition to blocking the straylight by the portion of the light shielding layer 302 located above thetop surface of the buried gate 118 a, the stray light may be furtherblocked by the extending portion 302 a of the light shielding layer 302.Therefore, the stray light interference may be further prevented.

FIG. 4 is a cross-sectional view of an image sensor according to anotherembodiment of the invention.

Please refer to FIG. 3C and FIG. 4, the differences between an imagesensor 400 and the image sensor 304 are as follows. In the image sensor400, the extending portion 402 a of the light shielding layer 402 may befurther extended to the dielectric layer 116. In addition, thearrangements, the materials, the forming methods, and the effects ofother components of the image sensor 400 of FIG. 4 have been illustratedin detail in the aforementioned embodiments, and the illustrations arenot repeated here.

Based on the aforementioned embodiment, in the image sensor 400, sincethe extending portion 402 a of the light shielding layer 402 may befurther extended to the dielectric layer 116, the stray light may beeffectively blocked from illuminating the storage node 108 to furtherprevent the stray light interference.

FIG. 5A to FIG. 5C are cross-sectional views of a manufacturing processof an image sensor according to another embodiment of the invention.FIG. 5A to FIG. 5C are cross-sectional views of the manufacturingprocess subsequent to the step of FIG. 1E.

Please refer to FIG. 5A, after the steps of FIG. 1E are performed, adielectric layer 500 may be formed on the light shielding layer 132. Inaddition, the dielectric layer 500 may further cover the gate structure122. A material of the dielectric layer 500 is, for example, siliconoxide. A forming method of the dielectric layer 500 is, for example,chemical vapor deposition.

An opening 502 may be formed in the dielectric layer 500, the lightshielding layer 132, and the buried gate 118 a. The opening 502 mayexpose the buried gate 118 a. A forming method of the opening 502 is,for example, removing a portion of the dielectric layer 500, a portionof the light shielding layer 132, and a portion of the buried gate 118 aby the lithography process and the etching process.

Please refer to FIG. 5B, a light shielding layer 504 filling in theopening 502 may be formed on the dielectric layer 500. As such, thelight shielding layer 504 may be formed on the buried gate 118 a. Thelight shielding layer 504 is located above the storage node 108 andelectrically connected to the buried gate 118 a. The light shieldinglayer 504 may have an extending portion 504 a. The extending portion 504a passes through the dielectric layer 500 and extends into the buriedgate 118 a. The extending portion 504 a may be located between the lightsensing device 106 and the storage node 108. A forming method of thelight shielding layer 504 is, for example, a combination of thedeposition process, the lithography process, and the etching process.The material of the light shielding layer 504 is, for example, a metalor a metal compound such as Ti, TiN, Ta, TaN, W, or Al.

In the present embodiment, although the light shielding layer 504 isillustrated as an example of the filling up opening 502, the inventionis not limited thereto. In another embodiment, under the condition thatthe thickness of the light shielding layer 504 is thinner, the lightshielding layer 504 may not fill up the opening 502.

Please refer to FIG. 5C, the dielectric layer 136, the interconnectstructure 138, the interconnect structure 140, the color filter layer142, and the microlens 144 may be formed on the substrate 100. Theinterconnect structure 140 passes through the dielectric layer 500 andelectrically connected to the gate 124. In addition, the manufacturingmethod of the dielectric layer 136, the interconnect structure 138, theinterconnect structure 140, the color filter layer 142, and themicrolens 144 in the image sensor 506 of FIG. 5C may be referred to theillustrations of FIG. 1F, and the illustrations thereof are not repeatedhere.

Moreover, in the aforementioned manufacturing method of the image sensor506, although the light shielding layer 132 may be formed between thedielectric layer 500 and the buried gate 118 a, the invention is notlimited thereto. In another embodiment, the light shielding layer 132may not be formed in the manufacturing method of the image sensor 506.

Hereinafter, the image sensor 506 of the present embodiment isillustrated with reference to FIG. 5C. In addition, although a formingmethod of the image sensor 506 is illustrated as an example of theaforementioned method, the invention is not limited thereto.

Please refer to FIG. 5C and FIG. 3C, the differences between the imagesensor 506 and the image sensor 304 are as follows. The image sensor 506may further include a dielectric layer 500. The dielectric layer 500 isdisposed between the light shielding layer 504 and the buried gate 118a. For example, the dielectric layer 500 may be disposed between thelight shielding layer 504 and the light shielding layer 132. Theextending portion 504 a passes through the dielectric layer 500 andextends into the buried gate 118 a. In the present embodiment, althoughthe bottom of the extending portion 504 a stays in the buried gate 118a, the invention is not limited thereto. In another embodiment, theextending portion 504 a may further extend to the dielectric layer 116.In addition, the materials, the arrangements, the conductive type, theforming methods, and the effects of other components of the image sensor506 in FIG. 5C illustrated in detail in the aforementioned embodiments,and the illustrations are not repeated here.

Based on the aforementioned embodiment, in the image sensor 506 and themanufacturing method thereof, the light shielding layer 504 may have theextending portion 504 a. In this way, in addition to blocking the straylight by the portion of the light shielding layer 504 located above thetop surface of the buried gate 118 a, the stray light may be furtherblocked by the extending portion 502 a of the light shielding layer 504.Therefore, the stray light interference may be further prevented.

In each of the aforementioned embodiments, although the gate structure122 is illustrated as an example of having the metal silicide layer 134,the invention is not limited thereto. In another embodiment, the gatestructure 122 may not have metal silicide layer 134.

In addition, although the image sensor of the aforementioned embodimentis illustrated as an example with one or two layers of light shieldinglayer, the invention is not limited thereto. In some embodiments, thenumber of layers of the light shielding layer may also be three or morelayers. That is, whether the number of layers of the light shieldinglayer is one or more layers is within the scope of the invention.

In summary, in the image sensor of the aforementioned embodiment and themanufacturing method thereof, since the buried gate is disposed in thesubstrate, the light shielding layer is disposed on the buried gate andlocated above the storage node. Therefore, the image sensor may use thelight shielding layer to block the stray light from illuminating thestorage node, thus the stray light interference can be effectivelyprevented.

Although the invention has been described with reference to theaforementioned embodiments, the invention is not limited to theaforementioned embodiments. It is apparent to one of ordinary skill inthe art that modifications and variations to the described embodimentsmay be made without departing from the spirit and scope of theinvention. Accordingly, the scope of the invention will be defined bythe attached claims.

What is claimed is:
 1. An image sensor, comprising: a substrate; a light sensing device, disposed in the substrate; a storage node, disposed in the substrate, wherein the storage node and the light sensing device are separated from each other; a buried gate structure, comprising: a buried gate, disposed in the substrate and covering at least a portion of the storage node; and a first dielectric layer, disposed between the buried gate and the substrate, wherein the first dielectric layer completely isolates the buried gate from the substrate; and a first light shielding layer, disposed on the buried gate and located above the storage node, wherein the first light shielding layer is electrically connected to the buried gate, the buried gate and the first light shielding layer are different materials, a portion of the buried gate is located directly above the storage node in a direction perpendicular to a top surface of the substrate, and a portion of the first light shielding layer is located directly above the storage node in the direction perpendicular to the top surface of the substrate.
 2. The image sensor according to claim 1, wherein a portion of the buried gate is located in the substrate between the light sensing device and the storage node.
 3. The image sensor according to claim 1, wherein a material of the first light shielding layer comprises a metal or a metal compound.
 4. The image sensor according to claim 1, further comprising a second light shielding layer, disposed on the first light shielding layer.
 5. The image sensor according to claim 1, wherein the first light shielding layer has an extending portion, and the extending portion extends into the buried gate.
 6. The image sensor according to claim 5, wherein the extending portion further extends to the first dielectric layer.
 7. The image sensor according to claim 5, wherein the extending portion is located between the light sensing device and the storage node.
 8. The image sensor according to claim 5, further comprising a third light shielding layer, disposed between the first light shielding layer and the buried gate.
 9. The image sensor according to claim 5, further comprising a second dielectric layer, disposed between the first light shielding layer and the buried gate, wherein the extending portion passes through the second dielectric layer and extends into the buried gate.
 10. The image sensor according to claim 1, further comprising a pinning layer, disposed in the substrate and located between the light sensing device and a surface of the substrate.
 11. The image sensor according to claim 1, further comprising: a gate structure, comprising: a gate, disposed on the substrate and located at one side of the buried gate away from the light sensing device, wherein the gate and the buried gate are separated from each other; and a third dielectric layer, disposed between the gate and the substrate; and a floating diffusion region, disposed in the substrate and located at one side of the gate structure away from the buried gate structure.
 12. The image sensor according to claim 1, further comprising: a color filter layer, disposed above the light sensing device; and a microlens, disposed on the color filter layer. 